This invention relates to apparatus and methods for chemical mechanical polishing and cleaning a substrate in an integrated system.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive or insulative layers on a silicon wafer. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.
After the substrate has been polished, it is typically cleaned, e.g., by a brush scrubber or megasonic cleaner, to remove excess slurry, polishing chemistry and other debris from the polishing process. After cleaning, the substrate is dried, e.g., by a spin-rinse drier, for return to the clean room. In some systems, e.g., systems that use the Marangoni effect, the cleaning and drying functions can be combined. Unfortunately, even after cleaning and drying, particles and other defects may remain on the substrate surface.
The chemical mechanical polishing and cleaning devices can be constructed as an integrated system with a single front-end automation interface between the clean room and the polishing and cleaning systems. An example of such an integrated system is the Mirra Mesa™ chemical mechanical polishing system from Applied Materials, Inc. of Santa Clara, Calif. Such an integrated system can include multiple ports to receive multiple cassettes at the interface with the clean room. Unfortunately, transport of the substrates between the cassettes and the polisher and cleaner can occasionally become backlogged, leading to a decrease in throughput.